Carbides are chemical compounds containing carbon and an element with lower electronegativity, or less of an ability to attract electrons. Nearly all elements react with elemental carbon to produce carbides. They are further classified into four groups: salt-like carbides, covalent carbides, interstitial carbides, and intermediate transition metal carbides. Salt-like carbides react with water and dilute acids to produce ions and hydrocarbon gases. Intermediate transition metal carbides also react with dilute acid and sometimes water to produce metallic cations, hydrocarbons and sometimes hydrogen.
Salt-like carbides are further broken down into methanides, acetylides, and sesquicarbides. Methanides react with water to produce methane. Methane is a carbon atom bonded to four hydrogen atoms in an sp3 hybridization. Two examples of methanides are aluminum carbide (Al4C3) and beryllium carbide (Be2C). Acetylides are salts of the acetylide anion C2−2 and also have a triple bond between the two carbon atoms. Triple bonded carbon has an sp1 hybridization and two examples of acetylides are sodium carbide (Na2C2) and calcium carbide (CaC2). Sesquicarbides contain the polyatomic anion C3−4 and contains carbon atoms with an sp1 hybridization. Two examples of sesquicarbides are magnesium (Mg2C3) and lithium (Li4C3).
U.S. Pat. No. 1,319,148 defined an oxidization reaction to produce potassium metal by reacting potassium cations (positive ions) with acetylide anions from calcium carbide. The reacting medium was molten potassium fluoride (mp=876° C.). This is shown in the reaction in Scheme (1) below.
The other products of this reaction are calcium fluoride and graphite. Graphite is the most thermodynamically stable form of elemental carbon, and this is therefore the favored product at high temperature. This reaction, the reduction of the potassium ion, takes place above 800° C. which would be considered high temperature since 600° C. is red heat.
Alkali metals can be prepared from electrolysis of molten salts. However, U.S. Pat. No. 1,319,148 indicates that an oxidization reaction was used to make alkali metals. Additionally, Concepts and Models of Inorganic Chemistry; Douglas B. McDaniel D. 1965 Xerox Corp. describes how they purified alkali metals before the electrolysis of the molten salts came into use.
To produce the alkali metal, the temperature is above the melting point of KF (mp=858° C.) which is high enough to vaporize K. (bp=744° C.). The products were indicated as being CaF2, K°, and the most thermodynamically stable form of carbon, graphite, C(graphite).